The invention relates an additive composition for a drilling fluid, as well as a method of increasing the lubricity and reducing the coefficient of friction of a drilling fluid. The additive composition may further contain a sulfurized olefin and/or a metal dithiophosphate compound, which further enhances the lubricating effect.
Drilling fluids, also referred to as drilling muds, are frequently circulated in a wellbore during drilling operations in order to cool and lubricate the drilling apparatus, lift cuttings out of the wellbore and counterbalance the subterranean formation pressure encountered during drilling. One of the functions of a drilling fluid is to reduce the considerable torque associated with the rotating drill stem caused by the friction between the outside of the drill pipe and the wall of the well and/or casing strings. Drilling through offsets, deep wells and highly deviated or horizontal wells results in increased frictional forces, increasing the demand on the lubricating properties of the drilling fluids.
Oil-based drilling muds (or “oil muds”) may be necessary or beneficial in certain circumstances, such as when drilling through formations containing expansive clays that swell upon contact with water. However, water-based drilling muds (also called “water muds”) are used much more commonly. Besides water, the main ingredient of a typical water mud is a viscosity agent, usually a fine-grained clay, which mixes with the water to form a slurry. Bentonite, which consists predominantly of an expansive clay called montmorillonite, is widely used in water muds, although other types of clay may be used as well.
In industry drilling operations, attempts have been made to reduce friction in drilling muds.